1. Field of the Invention
The present invention relates to a stencil printing machine which conveys a print medium while pressing the print medium to a drum on which a stencil sheet is mounted, and transfers ink oozing from perforations of the stencil sheet onto the print medium, and more particularly, to a technology for clamping a tip end of the stencil sheet by the drum.
2. Description of the Related Art
Such a type of stencil printing machine includes a stencil making unit which forms a perforated image on a stencil sheet, a printing unit which rotates a drum on which the stencil sheet having the perforated image formed thereon is mounted, conveys a print sheet while pressing the print sheet to the rotating drum, and transfers an ink image onto the print sheet, a paper feed unit which feeds the print sheet to the printing unit at predetermined timing, a paper discharge unit which discharges the print sheet printed by the printing unit to a predetermined position, and a stencil disposal unit which peels off the stencil sheet from an outer peripheral wall of the drum, and conveys the peeled-off stencil sheet into a stencil disposal box. Moreover, in order to neatly attach the stencil sheet having the perforated image formed thereon onto the drum without any slack or wrinkle, a stencil clamping portion is provided on the outer peripheral wall of the drum.
As a conventional example of the stencil clamping portion, there is one shown in FIG. 1 (in Japanese Patent Laid-Open Publication No. Hei 8-48069 (published in 1996). As shown in FIG. 1, such a stencil clamping portion 100 includes a stencil base 102 provided on an outer peripheral wall 101 of a drum, a magnet portion 103 provided on an inner surface side of the stencil base 102, and a clamping plate 104 which is supported so as to be freely rotatable with respect to the stencil base 102, and is shifted between a clamping position where the clamping plate 104 is absorbed to the stencil base 102 and a clamping release position where the clamping plate 104 is apart from the stencil base 102. The clamping plate 104 is moved by clamp moving means (not shown) on a machine body side.
In the configuration described above, when a tip end of a made stencil sheet 110 is conveyed to an upper surface of the stencil base 102, the clamping plate 104 is shifted from the clamping release position to the clamping position. Then, the clamping plate 104 is absorbed to the stencil base 102 by magnetic force of the magnet portion 103, and the tip end of the stencil sheet 110 is pinched between the clamping plate 104 and the stencil base 102. Specifically, the tip end of the stencil sheet 110 is clamped on the drum by the magnetic force of the magnet portion 103. Then, the outer peripheral wall 101 of the drum is rotated in a state where the drum clamps the tip end of the stencil sheet 110 thereon, and by this rotation of the outer peripheral wall 101, the stencil sheet 110 is wound around the outer peripheral wall 101, thus being loaded thereon.
However, in the conventional stencil clamping portion 100, the tip end of the stencil sheet 110 is sent out from a stencil making unit (not shown) to a position above the stencil base 102, and the stencil sheet 110 is mounted on the stencil base 102 in a state where no tension is applied thereto. Then, the clamping plate 104 moves by the rotation to the upper surface of the stencil sheet 110 to which no tension is applied, and clamps the stencil sheet 110. Accordingly, there is a possibility that the slack or the wrinkle occurs on the clamped stencil sheet 110. If the slack or the wrinkle occurs on the clamped stencil sheet 110, the stencil sheet 110 cannot be neatly attached onto the outer peripheral wall 101 of the drum without any slack or wrinkle.